(a) Field of the Invention
This invention generally relates to a universal safety release, or clutch, mechanism, and more particularly, but not by way of limitation, to a universal safety release for disengaging the drive mechanism to an overhead garage door having a counterbalance shaft.
(b) Discussion of the Prior Art
Many of today's automatic garage doors include a roll-up or swing-away type doors mounted on a counterbalance shaft that allows rotation of the door. The counterbalance shaft typically uses a large spring to react to the weight of the door, so that the door may be opened or closed with minimal effort or power.
Automatic garage doors also include some sort of an electric motor to provide the power that opens or closes the garage door. Present automatic garage door opening mechanisms are either of the center drive type or of the side mount type. With center drive mechanisms the electric motor drives a screw or a chain that in turn pulls on the top center area of the garage door. Side mounted systems, on the other hand, typically drive the counterbalance shaft in order to raise or lower the garage door.
There are many advantages to using a side mounted drive system. One of these advantages is that the side mounted system does not take up vertical space in the garage, and thus allows room for storage of taller vehicles. Another advantage is that the mechanism's drive unit can be mounted at the side of the garage entrance at a much lower, more accessible height than is required by the center drive. This facilitates maintenance and access to the drive mechanism in case of power failure or of mechanical failure of the drive mechanism.
Garage door drive mechanisms typically include some sort of drive disengagement device for disengagement of the drive mechanism when the unit is inoperative because of some sort failure. In center drive type of installations this disengagement mechanism is mounted somewhere along the mechanism that pulls on the central area of the garage door. However, a serious problem with this type of arrangement is that when the system fails with the door closed, and there is an automobile parked inside the garage, the user may have to climb on top of the car in order to reach the drive disengagement mechanism. This can place the user at risk of falling and injuring himself when trying to climb over the car, or can lead to damage to the vehicle. Also, the difficulties associated with disengaging the drive mechanism of a center drive may even cost precious time in emergency situations where power has been lost and the occupant of the home needs to escape the premises in a hurry. With side mounted devices, however, the drive mechanism can be mounted on the side of the garage where access to the drive disengagement mechanism is not a problem regardless of whether there is a vehicle in the garage.
The drive disengagement mechanism, therefore, is a very important safety element of the side mount mechanism. The drive disengagement mechanism must be very reliable and easy to access. Also, the disengagement mechanism should be easy to manufacture and install, and thus require few parts to operate.
The prior art includes several approaches at providing a drive disengagement mechanism for a side mount door drive. For example, U.S. Pat. No. 5,222,327 to Fellows et al. discloses a spring loaded disengagement system that permits sliding disengagement of a gear that is part of the gear drive train of a drive mechanism. The gear that permits disengagement in this arrangement is mounted on a splined hub that permits transmission of torque through the gear train. Because this system uses a gear train, each gear must be mounted on shafts with bearings or bushings, which makes manufacture and assembly somewhat complicated and expensive. Also, the gear train of the mechanism must be housed so that the gear and bearing surfaces are kept safely away from a user's extremities or from dust and contaminants that can shorten the life of the mechanism. Moreover, because the arrangement requires a housing the housing that must be used with a geared disengagement mechanism will also prevent easy examination of the components in order to trouble shoot the unit in case of a breakdown. Still further, the geared arrangement provides a fixed ratio of drive speed reduction due to the fact that gears have fixed diameter that require that the gear axles remain at fixed positions. This means that if a manufacturer or installer needs a slower or faster gear reduction, depending on the weight of the door and the application of the drive mechanism, one would probably have to provide an entirely new gear drive or install a different motor with a different motor speed control apparatus.
In yet another side mount door drive mechanism, U.S. Pat. No. 4,472,910 to Iha, shows a geared device including a gear having a set of integral raised projections that mate with an opening in a spring loaded rocker arm mounted on a pin that runs through the counterbalance shaft. One of the integral raised projections must be inserted into an opening in the rocker arm in order to transmit torque from the gear to the counterbalance shaft. This device is disadvantaged in that the system cannot be combined with other systems. In other words, the invention cannot be used in conjunction with other side mounted drive mechanisms, which limits the user's choice of sources of spare parts and components. Also, the Iha system is disadvantaged in that it uses a spring loaded rocker arm, which requires a rocker arm, two pins, a spring and an activation cam system in order to operate. This requires a large number of parts that must be manufactured, inventoried and maintained.
In yet another approach at solving the problems associated with disengaging the drive mechanism is the device taught by U.S. Pat. No. 3,512,302 to Sivin et al. The Sivin apparatus is a chain driven apparatus that includes a pair of sprockets that are connected together so that one sprocket serves to turn a shaft, like a counterbalance shaft, that supports and controls a overhead door. The other sprocket serves to control a limit switch. The two sprockets are tied to a drive motor by means of a pressure activated clutch, which can be engaged or disengaged by turning a threaded spindle against a pressure plate. The Sivin apparatus is simple and contains some inexpensive parts. For example, it uses chains and sprockets instead of gears. Also, it allows easy access to the clutch mechanism. However, the Sivin mechanism is disadvantaged in that it requires the use of many parts to produce the clutch mechanism. Also, in order to engage the clutch one must manually tighten a threaded spindle until it provides enough pressure against the clutch disks so as to prevent slippage. This brings to light one of the major disadvantages of the Sivin device. Many users may not be able to supply enough torque and hence pressure so as to prevent slippage. Also, temperature variations may cause expansion of the clutch elements so as to allow slippage after the mechanism had been tightened.
There remains, therefore, a need for a simple universal release mechanism for engaging and driving the door opening and closing mechanism of an automatic garage door. Importantly, there remains a need for a simple engagement mechanism that uses few parts, that can be used with side-mounted garage door drive mechanisms as well as other mechanisms manufactured by many different manufacturers, and can be easily accessed and operated regardless of whether a car is parked in the garage.